Research currently in progress concerns related morphological and physiological studies on an identified cell in the abdominal nerve cord of the crayfish, the caudal photoreceptor interneuron (CPR). The caudal photoreceptor can be uniquely identified from one experiment to the next on the basis of the anamolous light sensitivity of this pair of cells. In addition to its light sensitivity, this interneuron received direct monosynaptic input from tactile hairs and indirect polysynaptic, also of tactile origin, from other sensory regions. Direct monosynaptic input is excitatory in nature whereas the input from parallel interneurons is inhibitory. This research project is concerned with the integration of both sources of input in the production of directionally-sensitive coded spike outputs. In response to periodic water movements, the CPR integrates primarily input from telson and lateral uropod as determined by selective ablation of the roots of the 6th ganglion. Information from contralateral receptive fields is mediated by central inhibitory interneurons whose activity can be blocked by picrotoxin. The role of the CPR in behavioral reflexes is also being investigated. BIBLIOGRAPHIC REFERENCES: Wilkens, L.A., Larimer, J.L. (1976). Photosensitive interneurons in the 6th abdominal ganglion of decapod crustaceans: a comparative study. J. Comp. Physiol. (In press)